Fluorene based conjugated polymers are known to have optoelectronic properties. Several reports have demonstrated blue light emission from fluorene homopolymers e.g., A. W. Grice; D. D. C. Bradley, M. T. Bernius; M. Inbasekaran, W. Wu, E. P. Woo; Appl. Prep. Lett. 1998, 73, Y. Young and Q. Pei; J. Appl. Prep. 81, 3294(1997).
Attempts have been made to modify fluorene containing polymers to increase device efficiency. Attempts have also been made to control an undesired red shift in emission of polyfluorene based devices.
WO 01/81294 A1 teaches a fluorene polymer that is end-capped with a charge transporting tricyclic arylamine. That reference states that end-capping with at least one charge transporting moiety provides advantages. The purported advantages include higher efficiency and color stability without alteration of the electronic properties of the polyfluorene polymer main chain. The reference also states that approaches that include chemical moieties incorporated into the polyfluorene main chain or the copolymerization with other monomers inevitably modify essential properties of the main chain.
U.S. Pat. No. 5,874,179 (Kreuder et al) teaches optoelectronic polymers based on polyphenylenevinylene with nitrogen containing comonomers. Additionally, Kreudcr further teaches that fluorene could be part of a fused nitrogen containing ring structure in a polyphenylenevinylene based polymer.
U.S. Pat. No. 5,879,821 (Hsieh) teaches polymers containing repeat units of two tricyclic arylamines which are either bonded together or are arranged in a bis structure on either side of a divalent atom or moiety “G”. G can be O, S, N-Phenyl, vinylene, acetylene, p-phenylene, m-phenylene, o-phenylene, or —CH═CH—Phenyl —CH═CH—. A wide variety of additional units may be used with the two tricyclic aryl amine repeat units. Fluorene is included in a long list of additional units. However, Hsieh does not provide data relating to devices containing polymers of fluorene containing repeat units. Rather, the patent provides examples of devices based on acyclic triarylamine containing repeat units. The devices in Hsieh's examples are activated at very high voltages of 25V and 30 V.
A need remains for optoelectronic materials and devices that exhibit good conductivity, improved efficiency, emit a variety of colored light and have high brightness at low drive voltages.